[jira] [Commented] (METRON-1277) STELLAR Add Match functionality to language

["ASF GitHub Bot (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/METRON-1277?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16239665#comment-16239665 ] 

ASF GitHub Bot commented on METRON-1277:
----------------------------------------

Github user jjmeyer0 commented on the issue:

    https://github.com/apache/metron/pull/814
  
    @ottobackwards something is still going on with this. I'm seeing the following behavior:
    
    ```bash
    [Stellar]>>> foo := 500
    [Stellar]>>> match{ foo > 100 => ['oops'], foo > 200 => ['oh no'], foo >= 500 => MAP(['ok', 'haha'], (a) -> TO_UPPER(a)), default => ['a']}
    [!] Invalid parse, found [OK, HAHA]
    org.apache.metron.stellar.dsl.ParseException: Invalid parse, found [OK, HAHA]
            at org.apache.metron.stellar.common.StellarCompiler$Expression.apply(StellarCompiler.java:210)
            at org.apache.metron.stellar.common.BaseStellarProcessor.parse(BaseStellarProcessor.java:152)
            at org.apache.metron.stellar.common.shell.StellarExecutor.execute(StellarExecutor.java:292)
            at org.apache.metron.stellar.common.shell.StellarShell.handleStellar(StellarShell.java:282)
            at org.apache.metron.stellar.common.shell.StellarShell.execute(StellarShell.java:514)
            at org.jboss.aesh.console.AeshProcess.run(AeshProcess.java:53)
            at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
            at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
            at java.lang.Thread.run(Thread.java:748)
    [Stellar]>>> 
    ```


> STELLAR Add Match functionality to language
> -------------------------------------------
>
>                 Key: METRON-1277
>                 URL: https://issues.apache.org/jira/browse/METRON-1277
>             Project: Metron
>          Issue Type: New Feature
>            Reporter: Otto Fowler
>            Assignee: Otto Fowler
>
> From dev list:
> ------------
> Hi All, 
> It's high time that Stellar supports some form of conditional that is 
> beyond if/then/else. Right now, the way to do fall-through conditionals is: 
> if x < 10 then 'info' else if x >= 10 && x <= 20 then 'warn' else 'critical' 
> That becomes non-scalable very quickly. I wanted to facilitate a 
> discussion with the community on the syntax. I'll give a few options and 
> you guys/gals can come up with your own suggestions too, but I wanted to 
> frame teh conversation. 
> *MAP-BASED SWITCH* 
> With the advent of METRON-1254 (https://github.com/apache/metron/pull/801), 
> we could enable (from a language perspective in Stellar) multi-part 
> conditionals or switch/case style statements. To wit: 
> MAP_GET(true, { x < 10 : 'info', x >= 10 && x <= 20 : 'warn', x > 20 : 
> 'critical' }) 
> Or, with a convenience function: 
> CASE( { x < 10 : 'info', x >= 10 && x <= 20 : 'warn', x > 20 : 'critical' } 
> ) 
> The issue with this is that the last true condition wins because we're 
> using a map. 
> *LIST-BASED SWITCH* 
> We could correct this by adding a list of pairs construction to stellar: 
> CASE( [ x < 10 : 'info', x <= 20 : 'warn'], 'critical') 
> This would enable us to allow the first true condition to win, so the 
> second condition can be simpler and we could pass a default return value as 
> the final argument. 
> The downside to this, is that it requires a language enhancement (the list 
> of pairs construction you see there). 
> *LAMBDA FUNCTION-BASED SWITCH* 
> Some of the problems with the previous statements are that every 
> conditional has to be evaluated and there is no opportunity to short 
> circuit. They're all evaluated at parse-time rather than execution time. 
> We could, instead, construct a lambda function approach to this and support 
> short-circuiting in even complex conditionals: 
> CASE( real_variable_name, [ x -> x < 10 ? 'info', x -> x <= 20 ? 'warn' ], 
> 'critical') 
> or 
> CASE( real_variable_name, [ x -> if x < 10 then 'info', x -> if x <= 20 
> then 'warn' ], 'critical') 
> This would require lessening ?: (if/then/else) syntax to support to enable 
> just if without else conditions. This also has the benefit of allowing 
> simplifying the expression due to lambda function variable renaming 
> (real_variable_name can be much more complex (or even an expression) than 
> 'x'. 
> Creative other approaches to this are appreciated! 
> Thanks, 
> Casey 
> ----------------
> and ->
>  
> How about this:
> match(VAR_TO_VAL_ASSIGNMENT+) { BOOLEAN_STATEMENT(VALS) : LAMBDA(VALS), BOOLEAN_STATEMENT(VALS) : LAMBDA(VALS) , LAMBDA(VALS)}
> * match = new keyword
> * match takes variable number of assignments, where the val assigned to is available in the evaluation and the lambdas
> * match {} contains comma separated list of a statement that evaluates to a boolean and a lambda
> * LAMBDA is executed on match, and it’s value is returned
> * no matches returns null or return of optional final statement, which is a LAMBDA without a BOOLEAN_STATEMENT



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